Many child-resistant caps and closures have been suggested in recent years because of the greater activity directed toward insuring that dangerous and poisonous materials be packaged in containers which are significantly difficult for small children to open. At the same time, however, it is also necessary that the closures can be opened by an older child or an adult.
Many prior art closures of this general type are made child-resistant by the cooperative action of a radially or vertically extending tab carried by the cap and a lug formed on the shoulder or lower portion of the neck of the container against which the tab impinges when the child seeks to open the container by unscrewing the cap. Many of this type of child-resistant closures ignore a difficulty arising from the normal manufacturing tolerances which are present in both the cap and the bottle neck, in the threads on both, in the thickness of the liner or other sealing means interiorly of the cap, etc. When the tolerances which are built in during the manufacture accumulate, the result may be that if the cap closes a container for liquids, when a small child endeavors to open the container, he may twist the cap in an opening direction a distance sufficient to create a leaking container.
The foregoing problems are particularly prevalent when the cap is a screw type cap and is so designed as to be placed upon the container by automatic capping machinery of the type used for capping ordinary screw caps. Preferably, a child-resistant closure should be of a type which can be handled by standard capping equipment so that many such closures are made of the screw type hopefully to enable automatic capping without the necessity for the person filling the containers to buy new capping equipment.
Particularly where the closures are of the type which comprise a disc-like liner interiorly of the cap, the compressibility of the liner enters into the question of whether or not the cap is turned on to the bottle neck to the proper distance both to seal the container and to place the child-resistant elements in child-resistant position. Because of the tolerances mentioned above, it therefore becomes necessary to so design the cap and the container neck to insure that when the cap is put on to the container neck, for example by an automatic torque-responsive capping machine, it will be turned on to the neck far enough to at least engage the child-resistant means. Usually, therefore, it is turned on to the neck a distance beyond the engagement of the child-resistant means in order to insure that the container is sealed.
The problem arises the second time after the container has once been opened by an adult or older child who has then restored the cap to reseal the container. If this person turns the cap on to the neck of the container only until the child-resistant elements reach their engaging position, the cap may not be turned on to the neck tightly enough to prevent the container from leaking. If the person turns the cap on to the container neck sufficiently far to insure that it is sealed against leakage, the child-resistant means are spaced from each other, and a small child may rotate the cap in an unscrewing direction until the child-resistant means engage and, in doing so, may relieve the downward sealing thrust of the threads sufficiently so that it will leak.
Even if the counter rotation of the cap does not allow the cap to elevate greatly relative to the container neck, because most liners are not perfectly resilient, and because the finish on the end of the container neck may not be perfect, the counter rotation by the child up to the point of engagement of the locking means may result in the cap being loose on the container neck.
As an illustration of the problem, in a more or less standard six pitch thread, for every ten degrees of rotation of the cap relative to the bottle there is approximately 0.005 inch change in elevation of the cap. If the tolerances normally encountered in the fabrication of such caps and bottles are cumulated, then a 120.degree. retrograde rotation may be possible before the locking means abut, which will permit at least 0.055 inch elevation of the cap relative to the neck of the container.
It is also necessary to realize that when the cap is being threaded on to the container neck, the top surfaces of the cap threads bear against the under surfaces of the container neck threads. This thrusts the cap downwardly as it is rotated. Therefore, if the cap is rotated on to the container neck until it is tight and, particularly, when it must be rotated beyond the angular position at which the child-resistant means engage, the resulting problem is created.
With a normal screw type cap, when a person then endeavors to rotate the cap in a counter direction, i.e., seeking to unscrew the cap, the upper surfaces of the cap threads gradually disengage from the lower surfaces of the container neck threads and the cap is free to move up and down some fraction of an inch until continued rotation in the opening direction causes the engagement of the under surface of the cap threads with the upper surface of the container neck threads. This results from the fact that the vertical thickness of the threads on the interior of the cap cannnot be equal to the vertical space between the threads on the container neck. In order for the cap to be able to be screwed on to and off of the container, there must be clearance between the engaging surfaces of the two sets of threads and usually, to avoid unnecessary cap and bottle thread material, this clearance is a significant percentage of the space between the threads, say 35% or 0.06 inches.
It is in the interval between these two engagements that the cap is loose on the container neck and, with the six pitch thread, the cap may rotate 130.degree., 140.degree., or even 150.degree. before the elevating engagement of the lower surfaces of the cap threads and the upper surfaces of the container neck threads takes place. Rotation even of a few degrees, say 10.degree. or 15.degree., may be enough to result in a leaking container.
It is, therefore, the principal object of the instant invention to provide a screw type cap for the threaded neck of a container for liquids which is provided with a secondary cooperating means on the cap and container neck which hold the cap down in sealed position with sufficient force to prevent leakage from the container even when the cap has been rotated in an opening direction a distance such that it would otherwise have vertical play and a leaker might result.
It is a further object of the invention to provide a cap and a container neck equipped with cooperating cam means which exert downward thrust on the cap even when the cap has been rotated in an opening direction so as to disengage the upper surfaces of the cap threads and the lower surfaces of the container neck threads, thus holding the cap downwardly, holding the cap liner against the end of the container neck and maintaining the container in liquid sealed condition.